The present invention relates to self-attaching fasteners, a die button for use with such fasteners, a method of attaching such fasteners to a plate-like component, and the assembly which results after carrying out the method and the method of forming the improved self-attaching fasteners.
Fasteners of the general type having a hollow body or bore, such as for example internally threaded nuts are known from EP-A-0 553 822 A1 or from the corresponding US-A-5 340 251. Similar elements having hollow bodies are moreover known from US-A-3 234 987, from US-A-3 648 747 or from US-A-3 253 631.
All these known embodiments have a so-called pilot portion. That is to say that the groove or recess at the end face projecting toward the panel or part is restricted at the radially inner side by a projecting cylindrical pilot portion which extends at least substantially up to the end face.
Such fasteners are typically nut elements; however, for example they could have a cylindrical bore for receiving a spigot or the like. These fasteners offer relatively high security against rotation so that on screwing in a bolt element the fasteners remain firmly anchored to the component, and moreover have a relatively high resistance to push-out.
It has however been found that in operation with changing loads the fasteners sometimes tear out of the plate-like component which is normally made of sheet metal. Moreover the manufacture of such elements or fasteners having hollow bodies is relatively costly and a problem exists that the contact surface is frequently not adequate. Furthermore. the radial dimensions of the part engaging surface of the fastener make it necessary to use a relatively large washer at the bolt side in order to transmit the forces in the desired manner.
The undercut in the sidewall of the fastener recess which is necessary to generate the required press-out resistance of the hollow body, is normally generated in such a way that the hollow element is subjected to a squeezing process at the outer peripheral jacket with the sidewall of the recess being brought from an initially axial parallel position into an inclined position. This results in the opening to the recess between the pilot part and the now inclined sidewall to be smaller in comparison to the base surface of the recess. Additionally, as a result of this squeezing movement, the hollow element also has an inclined surface at the outer jacket surface adjacent to the end face engaging the component. On attachment to the plate-like component, the wedge-shaped contact surface, facing the plate-like component, is frequently so deformed that it acts in a knife-like manner under load and a high surface pressure results between the component and the hollow element.
As a result of this high surface pressure the plate-like component yields after a few operating hours and no longer sits as tightly as designed, so that the danger of settlement and of reduction of the preload to zero exists, and thus the danger of failure of the threaded connection.